Polyimide optical materials, polyimide precursor solutions and optical waveguide elements

ABSTRACT

Several novel polyimide materials are disclosed. One example is a polyimide material comprising heterocyclic polyimide having an unit represented by the following general formula (1):  
                 
         (wherein Φ 1 s may be the same or different and are individually a quadrivalent organic group, the Φ 1 s including at least 0.2 molar equivalent of a quadrivalent hetrocyclic group selected from the following Group (a), Ψ 1 s may be the same or different and are individually a bivalent organic group, and n is a positive integer).

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/10/684,474, filed Oct. 15, 2003, now allowed, and claims the benefitof priority from the prior Japanese Patent Application No. 2002-318239,filed Oct. 31, 2002, in which the entire contents of both areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to polyimide optical materials and anoptical waveguide element where the polyimide optical materials areemployed. In particular, the present invention relates to polyimidewhich is useful as an optical material for the optical waveguide of anoptoelectronic integrated circuit (OEIC) or of an optoelectronic mixedprinted wiring board and to an optical waveguide element where such apolyimide is employed.

2. Description of the Related Art

Organic polymer materials are advantageous over inorganic materials, inthat they are relatively light, excellent in impact resistance andworkability, and easy to handle. Because of such advantages, organicpolymer materials have been used extensively in optical components suchas optical fiber, lenses, and substrate for optical disks.

There is a problem, however, if the polymer materials are employed as amedium for enabling a near-infrared ray for optical communication totransmit therethrough, for example as an optical waveguide of an OEIC orof an optoelectronic mixed printed wiring board, the problem being arelatively large light transmission loss as compared with inorganicmaterials. The causes for this can be generally classified intoscattering and absorption. As the wavelength of light to be employed forthe optical communication is shifted to the longer wavelength side (from0.85 μm to 1.0 μm-1.7 μm), the infrared vibration which is intrinsic tothe molecular structure of polymer materials is increasingly lost byharmonic absorption and this loss of the infrared vibration becomespredominant. As a result, it is now feared that the application of thepolymer materials for use in the optical communication may becomedifficult.

In particular, polymethylmethacrylate (PMMA) and polystyrene (PS) whichhave been widely employed to date as an optical material for visiblelight, are formed of molecular structures having at least twocarbon-hydrogen bond (C—H bond) in their molecules. Therefore, thenear-infrared absorption spectra of these polymers include a pluralityof absorption peaks which are large in width and intensity. To shift theharmonic absorption originating from this C—H bond toward the longerwavelength side, to minimize the intensity of the harmonic absorption,the employment of deuterium (D) or fluorine (F) to substitute for theintramolecular hydrogen has been proved to be effective. With respect tothe materials where the hydrogen atoms in PMMA or PS are replaced bydeuterium or fluorine, there have been already conducted fundamentalstudies. However, since these polymeric optical materials are notprovided with sufficient soldering-heat resistance (260° C.) which isrequisite in the fabrication of OEIC on the surface of a siliconsubstrate for instance, various measures will be necessitated in thefabrication process if the these polymeric optical materials are to beactually employed in the fabrication of OEIC, etc.

On the other hand, polyimide resin is known as ordinarily having athermal decomposition temperature of as high as 400° C. or more, i.e. asone of the highest heat resistant resins among organic polymers, thus isnow being studied to employ polyimide resin as an optical material.

For example, a coating material made of a fluorine-containing polyimideresin having hexafluoroisopropylidene group is now being studied forusing it as a heat resistant material having an improved transparency.Further, there is proposed an optical waveguide formed of afluorine-containing polyimide resin having hexafluoroisopropylidenegroup in the main chain thereof for the purpose of minimizing the lighttransmission loss.

However, the polyimide materials that have been conventionally studied,such as partially fluorinated polyimide, are accompanied with thefollowing problems due to the fact that they contain a C—H bond of anaromatic ring in the molecular chain thereof. Namely, the near-infraredabsorption spectra of these polyimide materials include a peakoriginating from the harmonics of the stretching vibration of C—H bondor from a combination vibration formed between the harmonics of thestretching vibration of C—H bond and the bending vibration. As a result,it is impossible to achieve the minimization of light transmission lossthroughout the entire wavelength zone for optical transmission (1.0 μmto 1.7 μm).

Under the circumstances, it is now studied to employ, as a coatingmaterial, a fully fluorinated polyimide resin where all of hydrogenatoms in C—H bonds are substituted by fluorine atoms, and there isproposed an optical waveguide which is formed of this full fluorinatedpolyimide resin.

Although it is possible, with the employment of this full fluorinatedpolyimide resin, to achieve the minimization of light transmission lossthroughout the entire wavelength zone for optical transmission (1.0 μmto 1.7 μm), the hydrogen radicals thereof are all substituted byfluorine atoms, resulting in an excess introduction of fluorine atoms.Accordingly, due to this excess fluorine group, the solvent resistance,as well as the heat resistance, which are characteristic of theconventional polyimide material, are caused to greatly deteriorate inthis fully fluorinated polyimide resin, and at the same time, theworkability thereof for forming optical elements as well as the solderreflow property thereof are caused to greatly deteriorate, thusobstructing the utility of this fully fluorinated polyimide resin as amaterial for the manufacture of the optical waveguide of an opticalelement.

Although other fluorinated polyimides have been proposed, no one hassucceeded in providing an organic polymer material which is capable ofmeeting not only a high light transmitting property throughout theentire wavelength zone for optical communication but also otherproperties such as the solvent resistance and the heat resistance, allof which are required in the materials for manufacturing the opticalwaveguide of an optical element. Therefore, there is an earnest desireto develop an organic polymer optical material having all of theaforementioned properties.

Therefore, one of the objects of the present invention is to provide apolyimide optical material which is provided with sufficient heatresistance and solvent resistance demanded for the manufacture of anoptoelectronic integrated circuit and which can be employed as anorganic polymer optical material exhibiting an extremely low lighttransmission loss in the near infrared zone, in particular, throughoutthe entire wavelength zone for optical transmission (1.0 μm to 1.7 μm).

Another object of the present invention is to provide a polyimideprecursor solution that is useful for synthesizing the aforementionedpolyimide optical material.

A further object of the present invention is to provide an opticalwaveguide element which can be easily manufactured and is excellent inheat resistance and minimal in light transmission loss.

BRIEF SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided apolyimide material comprising heterocyclic polyimide having a repeatingunit represented by the following general formula (1), (2) or (3):

(wherein Φ₁s may be the same or different and are individually aquadrivalent organic group, the Φ₁s including at least 0.2 molarequivalent of a quadrivalent hetrocyclic group selected from thefollowing Group (a); Ψ₁s may be the same or different and areindividually a bivalent organic group; and n is a positive integer).

(wherein Φ₁s may be the same or different and are individually aquadrivalent organic group; Ψ₂s may be the same or different and areindividually a bivalent organic group, the Ψ₂s including at least 0.2molar equivalent of a bivalent hetrocyclic group selected from thefollowing Group (b); and n is a positive integer).

(wherein Φ₃s may be the same or different and are individually aquadrivalent organic group, the Φ₃s including at least 0.1 molarequivalent of a quadrivalent hetrocyclic group selected from thefollowing Group (a); Ψ₃s may be the same or different and areindividually a bivalent organic group, the Ψ₃s including at least 0.1molar equivalent of a bivalent hetrocyclic group selected from thefollowing Group (b); and n is a positive integer):Group (a):

Group (b):

(In the above formulas, X may be the same or different and areindividually >O group, >S group or >N—R^(f) group (R^(f) group isperfluoroalkyl group); R may be the same or different and areindividually fluoro group, chloro group, bromo group, iodo group,perfluoroalkyl group, perfluoroalkoxy group, perfluoroalkylthio group,nitro group or cyano group; m is an integer of 1 to 4)

According to another aspect of the present invention, there is provideda polyimide precursor solution comprising heterocyclic polyamic acidhaving a repeating unit represented by the following general formula(4), (5) or (6):

(wherein Φ₁s may be the same or different and are individually aquadrivalent organic group, the Φ₁s including at least 0.2 molarequivalent of a quadrivalent hetrocyclic group selected from thefollowing Group (a); Ψ₁s may be the same or different and areindividually a bivalent organic group; and n is a positive integer).

(wherein Φ₂s may be the same or different and are individually aquadrivalent organic group; Ψ₂s may be the same or different and areindividually a bivalent organic group, the Ψ₂s including at least 0.2molar equivalent of ambivalent hetrocyclic group selected from thefollowing Group (b); and n is a positive integer).

(wherein Φ₃s may be the same or different and are individually aquadrivalent organic group, the Φ₃s including at least 0.1 molarequivalent of a quadrivalent hetrocyclic group selected from thefollowing Group (a); Ψ₃S may be the same or different and areindividually a bivalent organic group, the Ψ₃s including at least 0.1molar equivalent of a bivalent hetrocyclic group selected from thefollowing Group (b); and n is a positive integer).Group (a):

Group (b):

(In the above formulas, X may be the same or different and areindividually >O group, >S group or >N—R^(f) group (R^(f) group isperfluoroalkyl group); R may be the same or different and areindividually fluoro group, chloro group, bromo group, iodo group,perfluoroalkyl group, perfluoroalkoxy group, perfluoroalkylthio group,nitro group or cyano group; m is an integer of 1 to 4)

According to another aspect of the present invention, there is providedan optical waveguide element comprising a core layer, and a clad layer,wherein the core layer and/or the clad layer comprise a polyimideoptical material of one embodiment of the present invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows an absorption spectrum of a polyimide film;

FIG. 2 is a cross-sectional view illustrating the structure of a buriedtype optical waveguide manufactured in one example;

FIG. 3 is a cross-sectional view illustrating the structure of a ridgetype optical waveguide manufactured in one example;

FIG. 4 is a plan view illustrating the structure of a star couplermanufactured in one example;

FIG. 5 is a schematic view illustrating the structure of a directionalcoupler manufactured in one example;

FIG. 6 is a perspective view illustrating the structure of athermooptical switch manufactured in one example;

FIG. 7 is a schematic view illustrating the structure of an arrayedwaveguide type optical multi-/demultiplexer manufactured in one example;

FIG. 8 is a plan view illustrating the structure of a grating type wavefilter manufactured in one example;

FIG. 9 is a perspective view illustrating the structure of abidirectional light transmitting module manufactured in one example;

FIG. 10 is a cross-sectional view illustrating the structure of aphotoelectric composite wiring board which was manufactured in oneexample; and

FIG. 11 is a perspective view illustrating a light modulator which wasmanufactured in one example.

DETAILED DESCRIPTION OF THE INVENTION

This invention will be further explained as follows.

To the Φ₁s and Φ₃s of the aforementioned general formulas (1) and (3), apredetermined quantity of a quadrivalent hetrocyclic group selected fromthe aforementioned Group (a) is required to be introduced. As for thequadrivalent hetrocyclic group, it is possible to employ, for example,pyrazinetetrayl group, pyridazinetetrayl group, furantetrayl group,thiophenetetrayl group, N-(perfluoroalkyl) pyrroletetrayl group,bioxazoletetrayl group, bithiazoletetrayl group, andN,N′-bis(perfluoroalkyl) bipyrazoletetrayl group. It is also possible toemploy, as the quadrivalent hetrocyclic group, pyridinetetrayl group,phenylene dioxazoletetrayl group and phenylene dithiazoletetrayl group,where all of hydrogen radicals in these groups are substituted by fluorogroup, chloro group, bromo group, iodo group, perfluoroalkyl group,perfluoroalkoxy group, perfluoroalkylthio group, nitro group or cyanogroup.

These quadrivalent hetrocyclic groups are required to be included as theΦ₁s in the compound of aforementioned general formula (1) at a ratio ofat least 0.2 molar equivalent and as the Φ₃s in the compound ofaforementioned general formula (3) at a ratio of at least 0.1 molarequivalent.

To the Ψ₂s and Ψ₃s of the aforementioned general formulas (2) and (3), apredetermined quantity of a bivalent hetrocyclic group selected from theaforementioned Group (b) is required to be introduced. As for thebivalent hetrocyclic group, it is possible to employ, for example,oxadiazoldiyl group, thiadiazoldiyl group, N-(perfluoroalkyl)triazoldiylgroup, bioxadiazoldiyl group, bithiadiazoldiyl group,N,N′-bis(perfluoroalkyl)bitriazolediyl group, thiazolothiazolediylgroup, and thiazolothienothiazoldiyl group. It is also possible toemploy, as the bivalent hetrocyclic group, pyridindiyl group,pyrimidindiyl group, pyrazindiyl group, pyridazindiyl, triazindiyl,benzobisoxazoldiyl, benzobisthiazoldiyl, phenylene dioxadiazoldiyl andphenylene dithiazoldiyl group, where all of hydrogen radicals in thesegroups are substituted by fluoro group, chloro group, bromo group, iodogroup, perfluoroalkyl group, perfluoroalkoxy group, perfluoroalkylthiogroup, nitro group or cyano group.

These bivalent hetrocyclic groups are required to be included as the Ψ₂sin the compound of afore-mentioned general formula (2) at a ratio of atleast 0.2 molar equivalent and as the Ψ₃s in the compound ofaforementioned general formula (3) at a ratio of at least 0.1 molarequivalent.

Namely, all of the hetrocyclic polyimides each having a repeating unitrepresented by any one of the aforementioned general formulas (1), (2)and (3) are required to include at least 0.2 molar equivalent ofspecific heterocyclic groups.

Since these heterocyclic groups contain no hydrogen radical, theheterocyclic polyimide materials to be obtained therefrom are free fromC—H bond which may become a cause for inviting loss of lighttransmission in the near infrared wavelength zone. Therefore, it ispossible to secure low light transmission loss throughout the entirewavelength zone for optical transmission (1.0 μm to 1.7 μm). Moreover,the resultant polyimide material will be prevented from beingexcessively introduced with fluorine atoms, thus making it possible toimprove the heat resistance and solvent resistance of the polyimidematerial. In order to sufficiently secure the aforementioned effects,the content of the heterocyclic group containing no hydrogen radicalshould preferably be controlled to at least 0.2 molar equivalent.

Further, although there is no particular limitation with regard to therange of the positive integer “n” in the aforementioned general formulas(1), (2) and (3), if “n” is too small, i.e. the molecular weight of thepolyimide is too small, it may not be possible to provide the polyimideresin with satisfactory coatability and heat resistance. On the otherhand, if “n” is too large, i.e. the molecular weight of the polyimide istoo large, the handling of the polyimide material would becomedifficult. In order to avoid the aforementioned problems, it ispreferable to confine “n” within the range of 5 to 200.

In the substituent groups shown in the aforementioned Groups (a) and(b), the range of “m” should preferably be within the range of 1 to 4.Because if “m” is 5 or more, the substituent group would becomeexcessively large, thereby possibly losing the excellent heatresistance, i.e. one of the inherent characteristics of polyimide.

The balance of the Φ₁s in the aforementioned general formula (1), thebalance of the Φ₃s in the aforementioned general formula (3) and the Φ₂sin the aforementioned general formula (2) may be constituted by thefollowing quadrivalent organic groups. Namely, they may be hydrocarbongroups including, for example, benzentetrayl group, naphthalentetraylgroup, perylentetrayl group, anthracentetrayl group, phenanthrentetraylgroup, pyrentetrayl group, biphenyltetrayl group, terphenyltetraylgroup, quaterphenyltetrayl group, quinquephenyltetrayl group,diphenylmethantetrayl group, diphenylethantetrayl group,diphenylpropantetrayl group, diphenylbutantetrayl group,diphenylpentantetrayl group, benzophenontetrayl group,diphenylethertetrayl group, diphenylsulfidtetrayl group,diphenylsulfontetrayl group, diphenyldimethylsilantetrayl group,diphenyltetramethyldisiloxantetrayl group, diphenoxybenzentetrayl group,diphenoxybiphenyltetrayl group, bis(phenoxyphenyl)ethertetrayl group,bis(phenoxyphenyl)sulfontetrayl group, bis(phenoxyphenyl)propantetraylgroup, anthraquinontetrayl group, phenathrenequinontetrayl group,fluorentetrayl group, fluorenontetrayl group, diphenylfluorentetraylgroup, xanthentetrayl group, ethantetrayl group, cyclopentantetraylgroup, cyclohexanetetrayl group, and bicyclohexyltetrayl group.

These quadrivalent organic groups may be substituted by the followingcharacteristic groups. Namely, examples of the characteristic groupsinclude di-substituted amino group (dimethylamino, diethylamino,dibutylamino, ethylmethylamino, butylmethylamino, diamylamino,dibenzylamino, diphenethylamino, diphenylamino, ditolylamino,dixylylamino, methylphenylamino and benzylmethylamino group);mono-substituted amino group (methylamino, ethylamino, propylamino,isopropylamino, tertbutylamino, anilino, anicisino, phenetidino,toluidino, xylidino, pyridylamino, thiazolylamino, benzylamino andbenzylideneamino group); cyclic amino group (pyrrolidino, piperidino,piperazino, morpholino, 1-pyrrolyl, 1-pirazolyl, 1-imidazolyl and1-triazolyl group); acylamino group (formylamino, acetylamino,benzoylamino, cinnamoylamino, pyridinecarbonylamino andtrifluoroacetylamino group); sulfonylamino group (mesylamino,ethylsulfonylamino, phenylsulfonylamino, pyridylsufonylamino,tosylamino, taurylamino, trifluoromethylsulfonylamino, sulfamoylamino,methylsulfamoylamino, sulfanylamino and acetylsulfanylamino group);amino group; hydroxyamino group; ureide group; semicarbazide group;carbazide group; di-substituted hydrazino group (dimethylhydrazino,diphenylhydrazino and methylphenylhydrazino group); mono-substitutedhydrazino group (methylhydrazino, phenylhydrazino, pyridylhydrazino andbenzylidenehydrazino group); hydrazino group; amidino group; oxime group(hydroxyiminomethyl, methoxyiminomethyl, ethoxyiminomethyl,hydroxyiminoethyl, hydroxyiminopropyl group, etc.); hydroxyl group; oxygroup (methoxy, ethoxy, propoxy, butoxy, hydroxyethoxy, phenoxy,naphthoxy, pyridyloxy, thiazolyloxy and acetoxy group); thio group(methylthio, ethylthio, phenylthio, pyridylthio and thiazolylthiogroup); alkoxyalkyl group (hydroxymethyl, hydroxyethyl and hydroxypropylgroup); cyano group; cyanate group; thiocyanate group; nitro group;nitroso group; mercapto group; halogen group (fluoro, chloro, bromo andiodo group); carboxyl group and the salts thereof; oxycarbonyl group(methoxycarbonyl, ethoxycarbonyl, phenoxycarbonyl and pyridyloxycarbonylgroup); aminocarbonyl group (carbamoyl, methylcarbamoyl,phenylcarbamoyl, pyridylcarbamoyl, carbazoyl, allophanoyl, oxamoyl andsuccinamoyl group); thiocarboxyl and the salts thereof; dithiocarboxyland the salts thereof; thiocarbonyl group (methoxythiocarbonyl,methylthiocarbonyl and methylthiothiocarbonyl group); acyl group(formyl, acetyl, propionyl, acryloyl, benzoyl, cinnamoyl,pyridinecarbonyl, thiazolecarbonyl and trifluoroacetyl group); thioacylgroup (thioformyl, thioacetyl, thiobenzoyl and pyridinethiocarbonyl);sulfinic acid radical and the salts thereof; sulfonic acid radical andthe salts thereof; sulfinyl group (methylsulfinyl, ethylsulfinyl andphenylsulfinyl group); sulfonyl group (mesyl, ethylsulfonyl,phenylsulfonyl, pyridylsulfonyl, tosyl, tauryl, trifluoromethylsulfonyl,sulfamoyl, methylsulfamoyl, sulfanilyl and acetylsulfanilyl group);oxysulfonyl group (methoxysulfonyl, ethoxysulfonyl, phenoxysulfonyl,acetaminopheoxysulfonyl and pyridyloxysulfonyl group); thiosulfonylgroup (methylthiosulfonyl, ethylthiosulfonyl, phenylthiosulfonyl,acetaminophenylthiosulfonyl and pyridylthiosulfonyl group);aminosulfonyl group (sulfamoyl, methylsulfamoyl, dimethylsulfamoyl,ethylsulfamoyl, diethylsulfamoyl, phenylsulfamoyl,acetaminophenylsulfamoyl and pyridylsulfamoyl group); ammonio group(trimethylammonio, ethyldimethylammonio, dimethylphenylammonio,pyridinio and quinolinio group); azo group (phenylazo, pyridylazo andthiazolylazo group); azoxy group; alkyl halide group (chloromethyl,bromomethyl, fluoromethyl, dichloromethyl, dibromomethyl,difluoromethyl, trifluoromethyl, pentafluoroethyl and heptafluoropropylgroup); organosilicic group (silyl, disilanyl, trimethylsilyl andtriphenylsilyl group).

The balance of the Ψ₂s in the aforementioned general formula (2), thebalance of the Ψ₃s in the aforementioned general formula (3) and the Ψ₁sin the aforementioned general formula (1) may be constituted by thefollowing bivalent organic groups. Namely, they may be hydrocarbongroups including, for example, phenylene group, naphthalendiyl group,perylendiyl group, anthracendiyl group, phenanthrendiyl group, pyrendiylgroup, biphenyldiyl group, terphenyldiyl group, quaterphenyldiyl group,quinquephenyldiyl group, diphenylmethandiyl group, diphenylethandiylgroup, diphenylpropandiyl group, diphenylbutandiyl group,diphenylpentandiyl group, benzophenondiyl group, diphenyletherdiylgroup, diphenylsulfidediyl group, diphenylsulfondiyl group,diphenyldimethylsilandiyl group, diphenyltetramethyldisiloxandiyl group,diphenoxybenzendiyl group, diphenoxybiphenyldiyl group,bis(phenoxyphenyl)etherdiyl group, bis(phenoxyphenyl)sulfondiyl group,bis(phenoxyphenyl)propandiyl group, anthraquinondiyl group,phenathrenequinondiyl group, fluorendiyl group, fluorenondiyl group,diphenylfluorendiyl group, xanthendiyl group, methylene group, ethyelenegroup, propylene group, cyclopentandiyl group, cyclohexandiyl group,bicyclohexyldiyl group and dipropyltetramethyldisiloxanediyl group.

These divalent organic groups may be substituted by the aforementionedcharacteristic groups.

The quadrivalent hetrocyclic groups to be introduced, as Φ₁s, into theaforementioned general formula (1) may be selected from quadrivalentaromatic hetrocyclic groups shown in the following Group (c), and thebalance of the Φ₁s may be selected from quadrivalentfluorine-substituted aromatic hydrocarbon groups shown in the followingGroup (e).Group (c):

Group (e):

The quadrivalent aromatic hetrocyclic substituent groups shown in theabove Group (c) can be introduced, as Φ₃, into the aforementionedgeneral formula (3), and the quadrivalent fluorine-substituted aromatichydrocarbon groups shown in the above Group (e) can be introduced, asΦ₂, into the aforementioned general formula (2) or, as the balance ofΦ₃, into the aforementioned general formula (3).

The bivalent organic groups to be introduced, as Ψ₁s, into theaforementioned general formula (1) may be selected from the bivalentfluorine-substituted aromatic hydrocarbon groups shown in the followingGroup (f).Group (f):

The bivalent fluorine-substituted aromatic hydrocarbon groups shown inthe above Group (f) can be introduced, as Ψ₂, into the aforementionedgeneral formula (2) or, as the balance of Φ₃, into the aforementionedgeneral formula (3).

The bivalent organic groups to be introduced, as Ψ₂s, into theaforementioned general formula (2) may be selected from the bivalentaromatic heterocyclic groups shown in the following Group (d).Group (d):

The bivalent aromatic hydrocarbon groups shown in the above Group (d)can be introduced, as Ψ₃, into the aforementioned general formula (3).

As already explained, the aromatic heterocyclic groups shown in theGroups (c) and (d) as well as the fluorine-substituted aromatichydrocarbon groups shown in the Groups (e) and (f) contain no hydrogenradical at all. Therefore, the heterocyclic polyimide materials to beobtained from a combination of these substituent groups are free fromC—H bond which may become a cause for inviting loss of lighttransmission in the near infrared wavelength zone or opticalcommunication zone. Therefore, it is possible to secure low lighttransmission loss throughout the entire wavelength zone for opticaltransmission (1.0 μm to 1.7 μm).

Due to the introduction of the aromatic heterocyclic groups shown in theGroups (c) and (d) into the polyimide material, it is possible toinhibit an excessive introduction of fluorine atoms. As a result, it isnow possible to suppress the deterioration of heat resistance andsolvent resistance of the polyimide material. Incidentally, in the caseof the conventional fully fluorinated polyimide, a difference inrefractive index among the substituent groups is relatively small, thusit has been difficult to alter the refractive index. Whereas, in thecase of the polyimide optical materials to be obtained according to theembodiments of the present invention, a difference in refractive indexbetween the aromatic heterocyclic groups shown in the Groups (c) and (d)and the full fluorine-substituted aromatic hydrocarbon group shown inthe Groups (e) and (f) is relatively large, so that it is possible,through the alteration of the ratio of these substituent groups to beintroduced, to optionally control the refractive index.

In the repeating units represented by the aforementioned generalformulas (1), (2) and (3), the content of fluorine atoms in eachrepeating unit should preferably be within the ratio of 5 to 40% byweight.

If the content of fluorine atoms in each repeating unit is larger than40% by weight, it may lead to a considerable degree of deterioration ofthe heat resistance and solvent resistance of the polyimide opticalmaterial to be obtained. On the other hand, if the content of fluorineatoms in each repeating unit is smaller than 5% by weight, it may leadto an increase in rate of moisture absorption of the polyimide opticalmaterial to be obtained, which may lead to the deterioration of theproperty of the polyimide material to secure low light transmission lossthroughout the entire wavelength zone for optical transmission. In orderto ensure better heat resistance, solvent resistance and anti-moistureabsorption property of the polyimide optical material to be obtained,the content of fluorine atoms in each repeating unit should preferablybe confined within the range of 15 to 35% by weight.

All of the hetrocyclic polyimides each having a repeating unitrepresented by any one of the aforementioned general formulas (1), (2)and (3) can be produced using, as a raw material, the heterocyclicpolyamic acids having a repeating unit represented by any one of thefollowing general formulas (4), (5) and (6).

Namely, the polyimide precursor solution according to the presentinvention is featured in that it comprises heterocyclic polyamic acidhaving a repeating unit represented by the following general formula(4), (5) or (6):

(wherein Φ₁s may be the same or different and are individually aquadrivalent organic group, the Φ₁s including at least 0.2 molarequivalent of a quadrivalent hetrocyclic group selected from thefollowing Group (a); Φ₁s may be the same or different and areindividually a bivalent organic group; and n is a positive integer).

(wherein Φ₂s may be the same or different and are individually aquadrivalent organic group; Ψ₂s may be the same or different and areindividually a bivalent organic group, the Ψ₂s including at least 0.2molar equivalent of a bivalent hetrocyclic group selected from thefollowing Group (b); and n is a positive integer).

(wherein Φ₃s may be the same or different and are individually aquadrivalent organic group, the Φ₃s including at least 0.1 molarequivalent of a quadrivalent hetrocyclic group selected from thefollowing Group (a); Ψ₃s may be the same or different and areindividually a bivalent organic group, the Ψ₃s including at least 0.1molar equivalent of a bivalent hetrocyclic group selected from thefollowing Group (b); and n is a positive integer).Group (a):

Group (b):

(In the above formulas, X may be the same or different and areindividually >O group, >S group or N—R^(f) group (R^(f) group isperfluoroalkyl group); R may be the same or different and areindividually fluoro group, chloro group, bromo group, iodo group,perfluoroalkyl group, perfluoroalkoxy group, perfluoroalkylthio group,nitro group or cyano group; m is an integer of 1 to 4)

To the Φ₁s and Φ₃s of the aforementioned general formulas (4) and (6), apredetermined quantity of a quadrivalent hetrocyclic group selected fromthe aforementioned Group (a) is required to be introduced. As for thequadrivalent hetrocyclic group, it is possible to employ the samehetrocyclic groups as illustrated with reference to the aforementionedgeneral formulas (1) and (3).

To the Ψ₂s and Ψ₃s of the aforementioned general formulas (5) and (6), apredetermined quantity of a bivalent hetrocyclic group selected from theaforementioned Group (b) is required to be introduced. As for thebivalent hetrocyclic group, it is possible to employ the samehetrocyclic groups as illustrated with reference to the aforementionedgeneral formulas (2) and (3).

The balance of the Φ₁s in the aforementioned general formula (4), thebalance of the Φ₃s in the aforementioned general formula (6) and the Φ₂sin the aforementioned general formula (5) may be constituted by theaforementioned substituted or unsubstituted hydrocarbon groups as aquadrivalent group.

The balance of the Ψ₂s in the aforementioned general formula (5), thebalance of the Ψ₃s in the aforementioned general formula (6) and the Ψ₁sin the aforementioned general formula (4) may be constituted by theaforementioned substituted or unsubstituted hydrocarbon groups as abivalent group.

As for the method of synthesizing the polyamic acid represented by theaforementioned general formulas (4) to (6), there is no particularlimitation, thus any method can be employed. It is particularlypreferable to employ a method wherein tetracarboxylic dianhydride and adiamine compound are polymerized in an inert gas atmosphere and in anorganic polar solvent without the presence of water.

On the occasion of introducing quadrivalent hetrocyclic groups shown inthe aforementioned group (a) into Φ₁s of the aforementioned generalformula (4) and into Φ₃s of the aforementioned general formula (6), itis possible to employ hetrocyclic tetracarboxylic dianhydride. Forexample, it is possible to employ heterocyclic tetracarboxylicdianhydrides, examples include unsubstituted heterocyclictetracarboxylic dianhydride such as pyrazine tetracarboxylicdianhydride, pyridazine tetracarboxylic dianhydride, furantetracarboxylic dianhydride, thiophene tetracarboxylic dianhydride,bioxazole tetracarboxylic dianhydride and bithiazole tetracarboxylicdianhydride; and substituted heterocyclic tetracarboxylic dianhydridesuch as pyridine tetracarboxylic dianhydride, phenylene bis(oxazoledicarboxylic) dianhydride, phenylene bis(thiazole dicarboxylic)dianhydride, bifuran tetracarboxylic dianhydride and bithiophenetetracarboxylic dianhydride, where all of hydrogen radicals in thesetetracarboxylic dianhydride, are substituted by a substituent group suchas halogen group, perfluoroalkyl group, perfluoroalkoxy group, nitrogroup or cyano group.

Especially preferable examples of the heterocyclic tetracarboxylicdianhydride include unsubstituted heterocyclic tetracarboxylicdianhydride such as pyrazine-2,3,5,6-tetracarboxylic dianhydride,pyridazine-3,4,5,6-tetracarboxylic dianhydride,furan-2,3,4,5-tetracarboxylic dianhydride,thiophene-2,3,4,5-tetracarboxylic dianhydride,2,2′-bioxazole-4,4′,5,5′-tetracarboxylic dianhydride and2,2′-bithiazole-4,4′,5,5′-tetracarboxylic dianhydride;4-fluoropyrizine-2,3,5,6-tetracarboxylic dianhydride;2-fluoropyrizine-3,4,5,6-tetracarboxylic dianhydride;4-(trifluoromethyl)pyrizine-2,3,5,6-tetracarboxylic dianhydride;2-(trifluoromethyl)pyrizine-3,4,5,6-tetracarboxylic dianhydride;2,3,5,6-tetrafluoro-1,4-phenylene-2,2′-bis(oxazole-4,5-dicarboxylic)dianhydride;2,3,5,6-tetrafluoro-1,4-phenylene-2,2′-bis(thiazole-4,5-dicarboxylic)dianhydride;2,4,5,6-tetrafluoro-1,3-phenylene-2,2′-bis(oxazole-4,5-dicarboxylic)dianhydride; and2,4,5,6-tetrafluoro-1,3-phenylene-2,2′-bis(thiazole-4,5-dicarboxylic)dianhydride.

On the occasion of introducing substituted or unsubstituted hydrocarbongroup as a quadrivalent substituent group into the balance of Φ₁s of theaforementioned general formula (4), into the balance of Φ₃s of theaforementioned general formula (6), and into Φ₂s of the aforementionedgeneral formula (5), it is possible to employ the followingtetracarboxylic dianhydride.

For example, it is possible to employ pyromellitic dianhydride, benzenetetracarboxylic dianhydride, benzophenone tetracarboxylic dianhydride,biphenyl tetracarboxylic dianhydride, terphenyl tetracarboxylicdianhydride, quaterphenyl tetracarboxylic dianhydride, methylenediphthalic dianhydride, ethylene diphthalic dianhydride, ethylidenediphthalic dianhydride, propylidene diphthalic dianhydride, trimethylenediphthalic dianhydride, tetramethylene diphthalic dianhydride,pentamethylene diphthalic dianhydride, hexafluoropropylidene diphthalicdianhydride, oxydiphthalic dianhydride, thiodiphthalic dianhydride,sulfonyl diphthalic dianhydride, bis(dicarboxyphenyl) tetramethylsiloxane dianhydride, bis(dicarboxyphenoxy)benzene dianhydride,bis[(dicarboxyphenyl)propyl]benzene dianhydride,bis[(dicarboxyphenoxy)phenyl]methane dianhydride,bis[(dicarboxyphenoxy)phenyl]propane dianhydride,bis[(dicarboxyphenoxy)phenyl]hexafluoropropane dianhydride,bis(dicarboxyphenoxy)dimethylsilane dianhydride,bis(dicarboxyphenyl)tetramethyldisiloxane dianhydride, naphthalenetetracarboxylic dianhydride, perylene tetracarboxylic dianhydride,pyrene tetracarboxylic dianhydride, anthracene tetracarboxylicdianhydride, phenanthrene tetracarboxylic dianhydride, anthraquinonetetracarboxylic dianhydride, phenanthrenequinone tetracarboxylicdianhydride, fluorenone tetracarboxylic dianhydride, ethylenetetracarboxylic dianhydride, butane tetracarboxylic dianhydride,cyclobutane tetracarboxylic dianhydride, cyclopentane tetracarboxylicdianhydride, cyclohexane tetracarboxylic dianhydride, bicyclohexyltetracarboxylic dianhydride, xanthene tetracarboxylic dianhydride, andbicycle[2,2,2]oct-7-ene tetracarboxylic dianhydride.

These tetracarboxylic dianhydrides may be substituted by any of theaforementioned characteristic groups.

As for the tetracarboxylic dianhydrides, especially preferable examplesinclude 3,6-difluoropyromellitic dianhydride,3,6-bis(trifluoromethyl)pyromellitic dianhydride,1,4,5,8-tetrafluoronaphthalene-2,3,6,7-tetracarboxylic dianhydride,2,3,6,7-tetrafluoronaphthalene-1,4,5,8-tetracarboxylic dianhydride,2,2′,5,5′,6,6′-hexafluorobiphenyl-3,3′,4,4′-tetracarboxylic dianhydride,oxy-4,4′-bis(3,5,6-trifluorophthalic) dianhydride,thio-4,4′-bis(3,5,6-trifluorophthalic) dianhydride,sulfonyl-4,4′-bis(3,5,6-trifluorophthalic) dianhydride,2,4,5,6-tetrafluoro-1,3-phenylenedioxy-4,4′-bis(3,5,6-trifluorophthalic)dianhydride,2,3,5,6-tetrafluoro-1,4-phenylenedioxy-4,4′-bis(3,5,6-trifluorophthalic)dianhydride, andoctafluoro-4,4′-biphenylenedioxy-4,4′-bis(3,5,6-trifluorophthalic)dianhydride.

These tetracarboxylic dianhydrides described above may be used singly orin combination of two or more.

On the occasion of introducing the bivalent hetrocyclic groups shown inthe aforementioned Group (b) into the Ψ₂s of the aforementioned generalformula (5), and into the Ψ₃s of the aforementioned general formula (6),it is possible to employ heterocyclic diamine compounds. For example, itis possible to employ unsubstituted heterocyclic diamines such asdiaminooxadiazole, diaminothiadiazole, diaminobioxadiazole,diaminobithiadiazole, diaminooxazooxazole, diaminooxazothiazole,diaminothiazolothiazole, diaminothiazolothienothiazole anddiaminothiazolopyrazinothiazole; and substituted heterocyclic diaminessuch as diaminopyrrole, diaminopyridine, diaminopyridazine,diaminopyrimidine, diaminopyrazine, diaminotriazine, phenylenebis(aminooxadiazole), phenylene bis(aminothiadiazole), phenylenebis(aminopyrazole), diaminobenzobisoxazole, diaminobenzobisthiazole,diaminofuran, diaminothiophene, diaminobioxazole and diaminobithiazolewhere all of hydrogen radicals other than amino group in theseheterocyclic diamines are substituted by a substituent group such ashalogen group, perfluoroalkyl group, perfluoroalkoxy group, nitro groupor cyano group.

Especially preferable examples of the heterocyclic diamine compoundsinclude 2,5-diamino-11,3,4-oxadiazole, 2,5-diamino-1,3,4-thiadiazole,3,5-diamino-1,2,4-oxadiazole, 3,5-diamino-1,2,4-thiadiazole,5,5′-diamino-2,2′-bi-1,3,4-oxadiazole,5,5′-diamino-2,2′-bi-1,3,4-thiadiazole,5,5′-diamino-3,3′-bi-1,2,4-oxadiazole,5,5′-diamino-3,3′-bi-1,2,4-thiadiazole,2,5-diaminothiazolo[5,4-d]thiazole,2,5-diaminothiazolo[4′,5′:3,2]thieno[4,5-d]thiazole,2,6-diamino-3,4,5-trifluoropyrizine, 4,6-diamino-2,5-difluoropyrimidine,2,6-diamino-3,5-difluoropyrazine, 2,6-diamino-4-fluorotriazine,2,6-diamino-4-(trifluoromethyl)triazine,2,3,5,6-tetrafluoro-1,4-phenylene-2,2′-bis(5-aminooxadiazole),2,3,5,6-tetrafluoro-1,4-phenylene-2,2′-bis(5-aminothiadiazole),2,4,5,6-tetrafluoro-1,3-phenylene-2,2′-bis(5-aminooxadiazole) and2,4,5,6-tetrafluoro-1,3-phenylene-2,2′-bis(5-aminothiadiazole).

On the occasion of introducing a substituted or unsubstitutedhydrocarbon group as a bivalent substituent group into the balance ofΨ₂s of the aforementioned general formula (5), into the balance of Ψ₃sof the aforementioned general formula (6), and into Ψ₁s of theaforementioned general formula (4), it is possible to employ thefollowing diamine compounds.

For example, it is possible to employ phenylene diamine,diaminobiphenyl, diaminoterphenyl, diaminoquaterphenyl,diaminoquinquephenyl, diaminonaphthalene, diaminoanthracene,diaminopyrene, diaminoperylene, diaminophenanthrene, oxydianiline,thiodianiline, sulfonyl dianiline, methylene dianiline, ethylenedianiline, propylidene dianiline, hexafluoropropylidene dianiline,hexafluoropropylene dianiline, bis(aminophenoxy)benzene,bis(aminophenylthio)benzene, bis(aminophenylsulfonyl)benzene,bis[(aminophenyl)propyl]benzene,bis[(aminophenyl)hexafluoropropyl]benzene, bis(aminophenoxy)benzene,bis[(aminophenoxy)phenyl]hexafluoropropane, bis(aminophenoxy)dimethylsilane, bis(aminophenyl)tetramethyl disiloxane, diaminofluorenone,bis(aminophenyl)fluorenone, methylene diamine, ethane diamine, propanediamine, butane diamine, pentane diamine, hexane diamine, heptanediamine, octane diamine, nonane diamine, decane diamine,bis(aminopropoxy)ethane, bis(aminopropyl)tetramethyl disiloxane,diaminocyclohexane, diaminobicyclohexyl, xylene diamine,bis(aminomethyl)cyclohexane, bis(aminopropyldimethylsilyl)benzene andbis(aminopropyl)tetraphenyldisiloxane.

These diamine compounds may be substituted by any of the aforementionedcharacteristic groups.

As for the diamine compounds, it is especially preferable to employtetrafluoro-1,3-phenylene diamine, tetrafluoro-1,4-phenylene diamine,octafluoro-4,4′-diaminobiphenyl, oxy-4,4′-bis(tetrafluoro)aniline,thio-4,4′-bis(tetrafluoro)aniline,sulfonyl-4,4′-bis(tetrafluoro)aniline,difluoromethylene-4,4′-bis(tetrafluoro)aniline,hexafluoro-2,2-propylidene-4,4′-bis(tetrafluoro)aniline,tetrafluoro-1,3-phenylenedioxy-4,4′-bis(tetrafluoro)aniline,octafluoro-4,4′-biphenylenedioxy-4,4′-bis(tetrafluoro)aniline.

These diamine compounds may be used singly or in combination of two ormore.

As for the organic polar solvent to be employed in the reaction, it ispossible to employ, for example, N,N-dimethylformamide,N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethoxyacetamide,N-methyl-2-pyrrolidone, N-acetyl-2-pyrrolidone, N-benzyl-2-pyrrolidone,1,3-dimethyl-2-imidazolidinone, hexamethylphosphortriamide,N-methyl-ε-caprolactam, N-acetyl-ε-caprolactam, 1,2-dimethoxyethane,1,2-diethoxyethane, bis(2-methoxyethyl)ether, bis(2-ethoxyethyl)ether,1,2-bis(2-methoxyethoxy)ethane, bis[2-(2-methoxyethoxy)ethyl]ether,1-acetoxy-2-methoxyethane, 1-acetoxy-2-ethoxyethane,(2-acetoxyethyl)(2-methoxyethyl)ether,(2-acetoxyethyl)(2-ethoxyethyl)ether, methyl 3-methoxypropionate,tetrahydrofuran, 1,3-dioxane, 1,3-dioxolane, 1,4-dioxane, pyrroline,pyridine, picoline, dimethylsulfoxide, sulfolane, γ-butyrolactone,propylene carbonate, phenol, cresol, acetone, methylethyl ketone,methylisobutyl ketone; cyclohexanone and acetonylacetone.

These organic solvents may be employed singly or in combination of twoor more. The temperature of the polymerization reaction may generally bein the range of −20 to 100° C., preferably in the range of −5 to 30° C.There is any particular limitation with respect to the reactionpressure, and hence the reaction can be performed satisfactorily undernormal pressure. The reaction time is dependent on the kind oftetracarboxylic dianhydride and also on the kind of the solvent to beemployed in the reaction. Generally, a time period of 1 to 24 hours maybe sufficient for the reaction. Incidentally, when it is difficult toincrease the degree of polymerization, it may be preferable to prolongthe reaction time to one to ten days, or to raise the reactiontemperature up to between 50° C. and 150° C.

The polyamic acid to be obtained in this case should preferably be 0.3(dL/g) or more, more preferably in the range of 0.3 (dL/g) to 3.0 (dL/g)in inherent viscosity, as it is turned into a 0.5 wt % solution of thepolyamic acid in N-methyl-2-pyrrolidone. Because, if the inherentviscosity of the polyamic acid is too low, i.e. if the polymerizationdegree of the polyamic acid is too low, it is difficult to obtain apolyimide resin having a sufficient heat resistance. On the other hand,if the inherent viscosity of the polyamic acid is too high, i.e. if thepolymerization degree of the polyamic acid is too high, the handling ofit would become difficult.

If it is desired to manufacture a film by using the heterocyclicpolyimide optical materials according to the embodiments of the presentinvention, it is possible to employ the conventional method ofmanufacturing a polyimide film. For example, a solution of theaforementioned precursor (polyamic acid) is coated on a substrate suchas a silicon wafer, and heated up stepwise starting from 150° C. up to350° C. (i.e. one hour at 150° C.—one hour at 250° C.—one hour at 350°C.) in an inert gas atmosphere such as nitrogen gas or argon gas, toturn the coated film into an imide film. Subsequently, the resultantimide film is peeled away from the substrate to obtain a heterocyclicpolyimide film.

Alternatively, the heterocyclic polyimide film can be manufactured by amethod wherein a heat cure promoter is added to a solution of theaforementioned precursor to enable the heterocyclic polyimide film to beobtained at relatively low temperatures and in a short period of time inair atmosphere or in an inert gas atmosphere. As for the heat curepromoter, it is possible to employ, for example, 4-hydroxypyridine,3-hydroxypyridine, 4-pyridine methanol, nicotinic-acid amide,isonicotinic-acid amide, picoline aldehydeoxime, nicotine aldehydeoxime, hydroxynicotinic acid, 2,2′-dipyridyl, 4,4′-dipyridyl, quinoline,isoquinoline, phenanthridine, imidazole, N-methyl imidazole,phthalazine, phenanthroline, benzimidazole, N-acetylglycine, hippuricacid, 3,5-dihydroxyacetophenone, pyrogallol, phloroglucinol, methylgallate, ethyl gallate, naphthalene-1,6-diol, 3-hydroxy benzoic acid and4-hydroxyphenyl acetate. It is possible, in this case, to manufacturethe heterocyclic polyimide film by heat-treating a coated layer of theprecursor solution at a temperature ranging from 150 to 250° C. for atime period ranging from about 10 minutes to 2 hours.

Further, in order to provide a polyimide film with various functions, afunctional pigment such as a non-linear optical pigment may be added toa solution of a precursor (polyamic acid). When the resultant solutionis coated on a substrate and heated, a heterocyclic polyimide filmhaving a functional pigment contained therein can be manufactured. Asfor the non-linear optical pigment, it is possible to employ, forexample, 4-[ethyl(2-hydroxyethyl)]amino-4′-nitroazobenzene,4-(dicyanovinyl)-4′-(dimethylamino)azobenzene,4-(diethylamino)-4′-(tricyanovinyl)azobenzene,4-(dimethylamino)-4′-nitrostilbene,4-(dimethylamino)-4′-(dicyanovinyl)stilbene,4-(dimethylamino)-4′-(tricyanovinyl)stilbene,4-methoxy-3-methyl-4′-nitrostilbene,N-(4-nitrobenzylidene)-3-(acetylamino)-4-methoxyanilinie,3-(acetylamino)-4-(dimethylamino)nitrobenzene,2-(cyclooctylamino)-5-nitropiperidine, N-(5-nitro-2-pyridyl)prolinol,2-[4-(diethylamino)styryl]-5-(tricyanovinyl)thiophene,1-[4-(diethylamino)phenyl]-4-[5-(tricyanovinyl)-2-thenyl]butadiene,1,3-diethyl-5-[5-(durolysin-9-yl)pentadienylidene]thiobarbituric acid,4-amino-4′-nitrodiphenyl sulfide,4-(dimethylamino)benzaldehyde=4-nitrophenyl hydrazone,4-(dimethylamino)benzaldehyde=5-nitro-2-pyridyl hydrazone and4-[4-(dimethylamino)benzylidene]-2-nitrophenyl-5-oxazolone.

These non-linear optical pigments can be added to a solution of apolyimide precursor at a mixing ratio of 2 to 30% by weight, forinstance.

Next, specific embodiments of optical waveguide elements according tothe present invention will be explained. In any of these embodiments, itis of course possible to apply them to a buried type, ridge type or slabtype optical waveguide structure.

As for the method of manufacturing an optical waveguide element by usinga polymer material, the following method is generally employed. Namely,a solution of a clad material is coated on the surface of a substrate bya spin coating method or dipping method to form a layer, which is thensubjected to a curing treatment as required to form a lower clad layer.On this lower clad layer thus obtained, a solution of a core material iscoated in the same way by spin coating method or dipping method to forma layer, which is then subjected to a curing treatment as required toform a core layer.

Further, by using fine working techniques such as photolithography anddry etching, a desired waveguide pattern is formed in the core layer.Finally, by a spin coating method or dipping method, a solution of cladmaterial is coated on the surface of the core layer to form a layer,which is then subjected to a curing treatment as required to form anupper clad layer. As a result of the aforementioned laminating process,an optical waveguide can be accomplished. Incidentally, the step offorming the optical waveguide pattern can be performed by using amold-working method or a drawing method, using for example aphotosensitive resin, as well as the aforementioned fine workingtechniques.

The polyimide optical materials according to the embodiments of thepresent invention can be employed for the manufacture of any of thelower clad layer, the core layer and the upper clad layer. If therefractive index can be differentiated, materials where the fundamentalstructure thereof is the same with each other can be employed for themanufacture of any of these components.

The optical waveguide elements to be manufactured as described above canbe utilized for the manufacture of a wavelength filter such as a linearwaveguide, a curved waveguide, a branched waveguide, a multiplexedwaveguide, an array type waveguide element and a grating type waveguideelement; and waveguide optical device such as a thermooptical switch, avariable light attenuator, bidirectional light transmitting module andan electrooptic modulator. Additionally, it is also possible to employthe aforementioned optical waveguide elements for the manufacture of anoptoelectric composite wiring board where a conventional electric wiringboard is provided with a light transmitting function.

Following are detailed explanations on specific examples of thisinvention. However, these examples should not be construed as limitingthe present invention.

(1) Synthesis of Polyamic Acid and Preparation of Polyimide Precursor:

Polyamic acid was synthesized as follows by using raw materials mixedtogether at a predetermined mixing ratio (shown in molar equivalent) asshown in the following Table 1. First of all, a predetermined quantityof tetracarboxylic dianhydride and a predetermined quantity of diaminecompound were placed in a reaction vessel (separable flask). Thisreaction vessel was cooled down to −5° C. to 5° C. by using a coolingmedium and 100 ml of N,N-dimethylacetamide was introduced little bylittle into the reaction vessel in an argon gas atmosphere with stirringto obtain a solution. Subsequently, the resultant solution was furtherstirred at room temperature for 24 hours in an argon gas atmosphere toobtain polyamic acid aimed at.

The raw materials (tetracarboxylic dianhydrides and diamine compounds)employed in Tables 1 to 4 and the synthesis schemes thereof are asfollows.

*PATA: 2,3,5,6-pyrazine tetracarboxylic dianhydride;

This PATA was synthesized according to the following scheme.

*PDTA: 3,4,5,6-pyridazine tetracarboxylic dianhydride;

This PDTA was synthesized according to the following scheme.

*FRTA: 2,3,4,5-furan tetracarboxylic dianhydride;

This FRTA was synthesized according to the following scheme.

*THTA: 2,3,4,5-thiophene tetracarboxylic dianhydride;

This THTA was synthesized according to the following scheme.

*6FPMA: 3,6-bis(trifluoromethyl)pyromellitic dianhydride;

This 6FPMA was synthesized according to the following scheme.

*6FBPTA: 2,2′,5,5′,6,6′-hexafluoro-3,3′,4,4′-biphenyl tetracarboxylicdianhydride;

This 6FBPTA was synthesized according to the following scheme.

*6FOPTA: oxy-4,4′-bis(3,5,6-hexafluorophthalic) dianhydride;

This 6FOPTA was synthesized according to the following scheme.

*6FPPTA: 1,1,1,3,3,3-hexafluoro-2,2-propylidene-4,4′-diphthalicdianhydride;

This 6FPPTA was obtained from the market.

*TDZDA: 2,5-diamino-1,3,4-thiadiazole;

This TDZDA was synthesized according to the following scheme.

*BTDZDA: 5,5′-diamino-2,2′-bi-1,3,4-thiadiazole;

This BTDZDA was synthesized according to the following scheme.

*BODZDA: 5,5′-diamino-3,3′-bi-1,2,4-oxadiazole;

This BODZDA was synthesized according to the following scheme.

*3FTAZDA: 2,4-diamino-6-trifluoromethyl-1,3,5-triazole;

This 3FTAZDA was synthesized according to the following scheme.

*4FmPDA: 2,4,5,6-tetrafluoro-1,3-phenylene diamine;

The product obtained from the market was refined.

*8FBPDA: 2,2′,3,3′,5,5′,6,6′-octafluoro-4,4′-biphenyl diamine;

This 8FBPDA was obtained from the market.

*8FODA: oxy-4,4′-bis(2,3,5,6-tetrafluoroaniline);

This 8FODA was synthesized according to the following scheme.

*6FBPDA: 2,2′-bis(trifluoromethyl)biphenyl-4,4′-diamine;

This 6FBPDA was obtained from the market.

*12FmAPB:1,3-bis(4-amino-2,3,5,6-tetrafluorophenoxy)-2,4,5,6-tetrafluorobenzene;

This 12FmAPB was synthesized according to the following scheme.

*12FpAPB:1,4-bis(4-amino-2,3,5,6-tetrafluorophenoxy)-2,3,5,6-tetrafluorobenzene;

This 12FpAPB was synthesized according to the following scheme.

The intrinsic viscosity of a 0.5 wt % N-methyl pyrrolidone solution ofeach of polyamic acids synthesized as described above was measured at atemperature of 30° C., the results being shown, together with the rawmaterials employed, in the following Tables 1 to 5. TABLE 1 ExampleExample Example Example Example 1 2 3 4 5 PATA 1.0 1.0 1.0 — — PDTA — —— 1.0 — FRTA — — — — 1.0 THTA — — — — — 6FPMA — — — — — 6FBPTA — — — — —6FOPTA — — — — — 6FPPTA — — — — — TDZDA — — — — — BTDZDA — — — — —BODZDA — — — — — 3FTAZDA — — — — — 4FmPDA 1.0 — — 1.0 1.0 8FBPDA — 1.0 —— — 8FODA — — 1.0 — — 6FBPDA — — — — — 12FmAPB — — — — — 12FpAPB — — — —— Concentra- 20.0  20.0  20.0  20.0  20.0  tion (wt %) Inherent  0.50 0.42  0.45  0.42  0.53 viscosity (dL/g)

TABLE 2 Example Example Example Example Example 6 7 8 9 10 PATA — — — —— PDTA — — — — — FRTA — — — — — THTA 1.0 1.0 0.5 — — 6FPMA — — — 1.0 —6FBPTA — — 0.5 — 1.0 6FOPTA — — — — — 6FPPTA — — — — — TDZDA — — — 1.01.0 BTDZDA — — — — — BODZDA — — — — — 3FTAZDA — — — — — 4FmPDA 1.0 — 1.0— — 8FBPDA — 1.0 — — — 8FODA — — — — — 6FBPDA — — — — — 12FmAPB — — — —— 12FpAPB — — — — — Concentra- 20.0  20.0  20.0  20.0  20.0  tion (wt %)Inherent  0.55  0.48  0.50  0.40  0.51 viscosity (dL/g)

TABLE 3 Example Example Example Example Example 11 12 13 14 15 PATA — —— — — PDTA — — — — — FRTA — — — — — THTA — — — — — 6FPMA — 1.0 — — —6FBPTA — — 1.0 — 1.0 6FOPTA 1.0 — — 1.0 — 6FPPTA — — — — — TDZDA 1.0 — —— — BTDZDA — 1.0 1.0 1.0 — BODZDA — — — — 1.0 3FTAZDA — — — — — 4FmPDA —— — — — 8FBPDA — — — — — 8FODA — — — — — 6FBPDA — — — — — 12FmAPB — — —— — 12FpAPB — — — — — Concentra- 20.0  20.0  20.0  20.0  20.0  tion (wt%) Inherent  0.47  0.44  0.53  0.49  0.42 viscosity (dL/g)

TABLE 4 Example Example Example Example Example 16 17 18 19 20 PATA — —0.5 1.0 1.0 PDTA — — — — — FRTA — — — — — THTA — 0.5 — — — 6FPMA — — 0.5— — 6FBPTA 1.0 0.5 — — — 6FOPTA — — — — — 6FPPTA — — — — — TDZDA — — 0.5— — BTDZDA 0.5 0.5 — — — BODZDA — — — — — 3FTAZDA 0.5 — — — — 4FmPDA —0.5 0.5 — — 8FBPDA — — — — — 8FODA — — — — — 6FBPDA — — — — — 12FmAPB —— — 1.0 — 12FpAPB — — — — 1.0 Concentra- 20.0  20.0  20.0  20.0  20.0 tion (wt %) Inherent  0.38  0.53  0.45  0.45  0.50 viscosity (dL/g)

TABLE 5 Example Example Comparative Comparative 21 22 example 1 example2 PATA — — — — PDTA — — — — FRTA — — — — THTA 1.0 1.0 — — 6FPMA — — 1.0— 6FBPTA — — — — 6FOPTA — — — — 6FPPTA — — — 1.0 TDZDA — — — — BTDZDA —— — — BODZDA — — — — 3FTAZDA — — — — 4FmPDA — — 1.0 — 8FBPDA — — — —8FODA — — — — 6FBPDA — — — 1.0 12FmAPB 1.0 — — — 12FpAPB — 1.0 — —Concentra- 20.0  20.0  20.0  20.0  tion (wt %) Inherent  0.50  0.53 0.38  0.65 viscosity (dL/g)

Among the polyamic acids obtained in Examples 1 to 22, those having arepeating unit represented by the aforementioned general formula (4)were polyamic acids obtained in Examples 1 to 8 and in Examples 19 to22; those having a repeating unit represented by the aforementionedgeneral formula (5) were polyamic acids obtained in Examples 9 to 16;and those having a repeating unit represented by the aforementionedgeneral formula (6) were polyamic acids obtained in Examples 17 and 18.

The polyamic acid obtained in Comparative Example 1 was a precursor offull fluorinated polyimide wherein all of hydrogen radicals in themolecule were substituted by fluorine and hence fluorine radicals wereexcessively introduced into the precursor. On the other hand, thepolyamic acid obtained in Comparative Example 2 was a precursor ofpartially fluorinated polyimide, so it included a hydrogen radical (C—Hgroup) in its molecule even in a state of polyimide after the heat curethereof.

(2) Preparation of Polyimide Film and the Measurement of the PhysicalProperties of the Polyimide Film:

By using a solution of each of the polyimide precursors (polyamic acids)obtained in Example 1 and Comparative Example 2, polyimide films wereprepared for using them for measuring the light absorption spectrumthereof. Specifically, first of all, a solution of each of the polyimideprecursors was coated on the surface of a silicon wafer 4 inches indiameter by a spin-coating method, and then the coated layer was heatedup stepwise from room temperature in a drying oven filled with nitrogengas. More specifically, each of the coated layers was heated for onehour at 150° C., for one hour at 250° C. and for one hour at 350° C.After being allowed to air-cool, the polyimide films were peeled awayfrom the silicon wafer to obtain polyimide films for using them formeasuring the light absorption spectrum thereof. After being allowed todry in vacuum for two hours at a temperature of 100° C., these polyimidefilms were measured with regard to the light absorption spectrum thereofin the range of 0.6 to 1.7 μm in wavelength.

The results of the measurement on the light absorption spectrum of eachof polyimide films are shown in the graph of FIG. 1. In FIG. 1, thecurves “a” and “b” illustrate the results of the measurement of thepolyimide films of Example 1 and Comparative Example 1, respectively.Incidentally, in the graph of FIG. 1, the abscissa represents thewavelength (μm) and the ordinate represents the light absorbency(arbitrary unit).

It is clearly demonstrated by the curve “a” that the polyimide film ofExample 1 was incapable of absorbing light in the wavelength range of1.0 to 1.6 μm. Whereas, as shown in the curve “b”, the partiallyfluorinated polyimide of Comparative Example 2 was capable of absorbingthe light of this wavelength zone. It was confirmed from these resultsthat the polyimide films according to Examples of the present inventionwere excellent in light transparency in the wavelength zone of opticalcommunications.

Next, polyimide films for using them for measuring the thermogravimetricanalysis/differential thermal analysis (TG/DTA), thermomechanicalanalysis (TMA), water absorption and solvent resistance thereof weremanufactured according to the following procedure. Specifically, firstof all, a solution of each of the polyimide precursors was coated on thesurface of a glass plate having a size of: 1 mm×130 mm×150 mm by using abar coater having a thickness of 75 μm, and then the coated layer washeated for one hour at a temperature of 110° C. The polyamic acid filmthus obtained was peeled away from the glass substrate and secured to abrass frame having an inner frame dimension of: 100 mm×100 mm. Theresultant structure was heated up stepwise from room temperature in adrying oven filled with nitrogen gas. More specifically, each of thecoated layers was heated for one hour at 150° C., for one hour at 250°C. and for one hour at 350° C. to obtain polyimide films.

According to the following methods, these polyimide films thusmanufactured were measured with regard to the decomposition temperature,glass transition temperature (Tg), moisture absorption and solventresistance thereof.

Namely, the decomposition temperature (5 wt % weight reductiontemperature) of the polyimide films TABLE 6 Ratio of Glass Moisturefluorination Transparency Decomposition transition absorbency (wt %)1.0-1.6 μm temp. (° C.) temp. (° C.) (%) Solvent resistance Example 120.9 Not absorbed 530 330 0.4 Not dissolved/not changed Example 2 29.7Not absorbed 520 340 0.4 Not dissolved/not changed Example 3 28.8 Notabsorbed 520 300 0.5 Not dissolved/not changed Example 4 20.9 Notabsorbed 510 315 0.4 Not dissolved/not changed Example 5 21.6 Notabsorbed 535 330 0.3 Not dissolved/not changed Example 6 20.7 Notabsorbed 540 335 0.3 Not dissolved/not changed Example 7 29.5 Notabsorbed 535 340 0.3 Not dissolved/not changed Example 8 29.1 Notabsorbed 530 310 0.3 Not dissolved/not changed Example 9 26.3 Notabsorbed 510 310 0.4 Not dissolved/not changed Example 10 23.7 Notabsorbed 525 320 0.4 Not dissolved/not changed Example 11 22.9 Notabsorbed 520 300 0.5 Not dissolved/not changed Example 12 22.0 Notabsorbed 510 315 0.4 Not dissolved/not changed Example 13 20.1 Notabsorbed 530 320 0.4 Not dissolved/not changed Example 14 19.6 Notabsorbed 525 305 0.5 Not dissolved/not changed Example 15 21.3 Notabsorbed 530 320 0.4 Not dissolved/not changed Example 16 25.7 Notabsorbed 515 310 0.3 Not dissolved/not changed Example 17 20.3 Notabsorbed 530 310 0.3 Not dissolved/not changed Example 18 23.8 Notabsorbed 525 305 0.3 Not dissolved/not changed Example 19 32.9 Notabsorbed 510 300 0.3 Not dissolved/not changed Example 20 32.9 Notabsorbed 515 305 0.3 Not dissolved/not changed Example 21 32.7 Notabsorbed 520 300 0.3 Not dissolved/not changed Example 22 32.7 Notabsorbed 525 305 0.3 Not dissolved/not changed Comparative 38.2 Notabsorbed 490 220 0.3 Dissolved example 1 Comparative 31.1 Absorbed 530335 0.4 Swelled example 2was measured in a nitrogen gas stream by TG/DTA. The glass transitiontemperature (Tg) of the polyimide films was measured by TMA. Themoisture absorption of the polyimide films was measured in such a mannerthat the polyimide films were left to stand for one week in anatmosphere of saturated water vapor at a temperature of 20° C. and then,the water collected on the surfaces of the films was wiped away andmeasured by tube oven-attached Karl Fischer water content titratingmethod. Further, the solvent resistance of the polyimide films wasmeasured in such a manner that a piece of the polyimide film having asize of: 10 mm×30 mm is placed in a flask, into which 50 mL ofN,N-dimethylacetoamide (DMAC) is introduced and stirred for one hour ata temperature of 30° C. to visually observe any changes in theconfiguration of the polyimide film.

The results obtained are shown in the following Table 6 together withthe rate of fluorination and optical transparency of each of thesepolyimide films.

As shown in Table 6, the polyimide films according to these Examples ofthe present invention (Examples 1 to 22) were found excellent in all ofthe properties including the decomposition temperature, glass transitiontemperature (Tg), moisture absorption and solvent resistance.

Specifically, the polyimide films of Examples 1 to 22 were all found ashaving a very high decomposition temperature ranging from 510° C. to540° C. which is comparative to that of the fluorinated polyimides ofComparative Examples 1 and 2, thus confirming the excellent heatdecomposition resistance of these polyimide films of Examples 1 to 22.Further, the glass transition temperature of the polyimide films ofExamples 1 to 22 were all found as having a very high glass transitiontemperature ranging from 300° C. to 340° C., which is higher than thatof the full fluorinated polyimide of Comparative Example 1 andcomparable to that of the partially fluorinated polyimide of ComparativeExample 2, thus confirming the excellent heat resistance of thesepolyimide films of Examples 1 to 22.

With respect to the moisture absorption, the polyimide films of Examples1 to 22 were all found very low in moisture absorption, i.e. within therange of 0.3 to 0.5%, which is comparable to that of the fluorinatedpolyimides of Comparative Examples 1 and 2, thus confirming theexcellent anti-moisture absorption property of these polyimide films ofExamples 1 to 22.

Moreover, the polyimide films of Examples 1 to 22 indicated littlechanges in configuration as a result of the aforementioned solventresistance test. Whereas, the full fluorinated polyimide of ComparativeExample 1 was found completely dissolved in the DMAC, and the partiallyfluorinated polyimide of Comparative Example 2 was found swelled in theDMAC. In view of these facts, the polyimide films of Examples 1 to 22were excellent in solvent resistance, thus confirming the excellentsolvent resistance of the heterocyclic polyimides of these examples ofthe present invention.

Next, by using the heterocyclic polyimide precursors according to theexamples of the present invention, various kinds of optical waveguideelements were manufactured.

EXAMPLE 23

FIG. 2 shows a cross-sectional view illustrating the structure of aburied type optical waveguide manufactured in this example. In thisburied type optical waveguide shown in FIG. 2, a lower clad layer 2 andan upper clad layer 3 were successively laminated on the surface of asilicon wafer employed as a substrate 1. In this structure, a core 4 isburied in the upper clad layer 3.

The lower clad layer 2, the upper clad layer 3 and the core 4 were allformed by using polyamic acid varnish which was prepared in advance insuch a manner that to a solution comprising, as a fundamentalconstituent compound, the heterocyclic polyimide precursor prepared inthe aforementioned Example 6, 4-hydroxypyridine was added as a heat curepromoter at a ratio of 10% by weight based on the solid matter in thesolution to obtain the varnish. The heterocyclic polyimide precursor forforming each of the aforementioned components was respectivelysynthesized by changing the composition of raw material so as to enablethe refractive index of the polyimide film after curing to fall within adesired range.

First of all, a solution of the heterocyclic polyimide precursor forforming the lower clad layer was coated on the surface of the siliconwafer 1 by spin coating and heated for about 30 minutes at a temperatureof 200° C. to form the lower clad layer 2 having a thickness of about 5μm. On this lower clad layer 2, a solution of the heterocyclic polyimideprecursor for forming the core layer was coated in the same manner asdescribed above and heated for about 30 minutes at a temperature of 200°C. to form a polyimide layer having a thickness of 8 μm. Byphotolithography and dry etching, the polyimide layer was patterned toform the core layer 4 having a width of 8 μm.

A solution of the heterocyclic polyimide precursor for forming the upperclad layer was coated all over the lower clad layer 2 and the core layer4 in the same manner as described above and heated for about 30 minutesat a temperature of 200° C. to form an upper clad layer 3 having athickness of about 5 μm.

As a result of the aforementioned process, a buried type channelwaveguide having a size of: 8 μm (in width)×8 μm (in height) was formedas shown in FIG. 2.

The buried type optical waveguide thus obtained was cut out by dicingand the optical characteristics thereof were evaluated. As a result ofthe evaluation of the light transmission loss of the optical waveguideby cutback method, the light transmission loss was found to be 0.2 dB/cmfor TM polarized wave and 0.16 dB/cm for TE polarized wave.

When the buried type optical waveguide was baked in a dry atmosphere ata temperature of 200° C. to investigate the heat resistance thereof, thecharacteristics of the optical waveguide were not fluctuated even afterthe baking of 500 hours. Further, when a pressure cooker test (120° C.,100% RT and 2 atm.) was performed as a life test, the fluctuation incharacteristics of the optical waveguide was not recognized at all.

EXAMPLE 24

FIG. 3 shows a cross-sectional view illustrating the structure of aridge type optical waveguide manufactured in this example. In this ridgetype optical waveguide shown in FIG. 3, a lower clad layer 2 and a corelayer 4 were successively deposited on the surface of a silicon waferemployed as a substrate 1.

The lower clad layer 2 and the core 4 were all formed by using asolution which was prepared in the same manner as that of aforementionedExample 23.

First of all, a solution of the heterocyclic polyimide precursor forforming the lower clad layer was coated on the surface of the siliconwafer 1 by spin coating and heated for about 30 minutes at a temperatureof 200° C. to form the lower clad layer 2 having a thickness of about 5μm. On this lower clad layer 2, a solution of the heterocyclic polyimideprecursor for forming the core layer was coated in the same manner asdescribed above and heated for about 30 minutes at a temperature of 200°C. to form a polyimide layer having a thickness of 5 μm. Byphotolithography and dry etching, the polyimide layer was patterned toform the core layer 4 having a width of 8 μm.

As a result of the aforementioned-process, a ridge type channelwaveguide having a size of: 8 μm (in width)×5 μm (in height) was formedas shown in FIG. 3.

The ridge type optical waveguide thus obtained was cut out by dicing andthe optical characteristics thereof were evaluated. As a result of theevaluation of the light transmission loss of the optical waveguide bycutback method, the light transmission loss was found 0.3 dB/cm for TMpolarized wave and 0.28 dB/cm for TE polarized wave.

When this ridge type optical waveguide was baked in a dry atmosphere ata temperature of 200° C. to investigate the heat resistance thereof, thecharacteristics of the optical waveguide were not fluctuated even afterthe baking of 500 hours. Further, when a pressure cooker test (120° C.,100% RT and 2 atm.) was performed as a life test, the fluctuation incharacteristics of the optical waveguide was not recognized at all.

EXAMPLE 25

FIG. 4 shows a plan view illustrating the structure of a star couplermanufactured in this example.

An optical waveguide layer 5 was manufactured by using the technique ofburied type waveguide structure and by the same way as that described inExample 23 using a solution of the heterocyclic polyimide precursorwhich was prepared in the same manner as described in Example 23. Thestar coupler shown in FIG. 4 is a 1×16 star coupler which enables theequipartition of optical signals to be realized.

When a beam of light having a wavelength of 1.55 μm was irradiated froman incidence port 6, it was possible to detect optical signals having anintensity of about 1/16 from all of outgoing ports 7.

EXAMPLE 26

FIG. 5 shows a schematic view illustrating the structure of adirectional coupler manufactured in this example.

An optical waveguide layer 8 was manufactured by using a buried typewaveguide structure and by the same way as that described in Example 23using a solution of the heterocyclic polyimide precursor which wasprepared in the same manner as described in Example 23.

As an optical fiber was coupled with an input port 9 of the directionalcoupler obtained in this example, it was possible to enable an outputport 10 to have an output of light. When the wavelength of beam to beirradiated is 1.55 μm, the coupling ratio of TM polarized wave and TEpolarized wave was 97% or more. Further, on this occasion, the insertionloss including the coupling loss was 2 dB, and the excessive loss of 3dB coupler was 0.2 dB, thus both indicating excellent characteristics.

Further, the directional coupler according to this example washeat-treated for 100 hours at a temperature of 100° C. and then, left tostand in an atmosphere of high temperature and high humidity (85° C., 85RH). Even after the exposure to such severe conditions, the directionalcoupler was confirmed as capable of maintaining the same degree ofperformance as the initial performance thereof and of exhibiting stableproperties.

EXAMPLE 27

FIG. 6 shows a perspective view illustrating the structure of athermooptical switch manufactured in this example. In this thermoopticalswitch shown in FIG. 6, an optical waveguide layer 12 and heaterelectrodes 13 were formed on the surface of a substrate 11.

The optical waveguide layer 12 was formed by using a solution which wasprepared in the same manner as that of aforementioned Example 23. Thesize of the core was set to 8 μm×8 μm, and the planar structure ofbranched paths was formed of a Y-shaped structure where the branch anglethereof was set to 0.1 degree. On the surface of the upper clad layer,Ti was deposited to a thickness of 50 nm, and then, Pt was deposited toa thickness of 200 nm, both by vacuum deposition. The resultant layerswere patterned by photolithography and ion milling, thereby forming thinfilm heater electrodes 13.

As a result of the aforementioned process, a digital type 1×2thermooptical light switch was formed as shown in FIG. 6. Thethermooptical light switch thus manufactured was cut out by dicing toform a chip-like switch for evaluating the optical properties thereof.

When a beam of light having a wavelength of 1.55 μm was introduced,through an optical fiber, into this manufactured thermooptical lightswitch under the condition where electric current is not transmitted toany of the heater electrodes 13, both of the output ports were enabledto have an output of a half of the light, respectively. On the otherhand, when electric current, i.e. an electric power of about 100 mW, istransmitted to only one of the heater electrodes, only one of the outputports which was not lightened was permitted to have an output of thelight, thus confirming the switching. On this occasion, the quenchingratio was 20 dB and the switching velocity was 10 msec.

Even when the operation of alternately applying an electric power of 100mW to the heaters was repeated 10⁴ times, there was not recognized anysubstantial change in durability of the heaters.

EXAMPLE 28

FIG. 7 shows a schematic view illustrating the structure of an arrayedwaveguide type optical multi-/demultiplexer manufactured in thisexample. This arrayed waveguide type optical multi-/demultiplexer shownin FIG. 7 was manufactured by using the technique of buried typewaveguide structure and by the same way as that described in Example 23using a solution of the heterocyclic polyimide precursor which wasprepared in the same manner as described in Example 23.

In this arrayed waveguide type optical multi-/demultiplexer, wavelengthmultiple signals having wavelengths of λ₁, λ₂ . . . λ₈ which have beenintroduced therein from an input port 15 are permitted to spatiallyexpand by an input slab 16 functioning as a lens and then, coupled ontoan arrayed waveguide 14. Since this arrayed waveguide 14 is providedwith the function of grating, eight signals are enabled to diffract indifferent directions depending on differences in wavelength. At anoutput slab 17, the signal lights that have been diffracted inaccordance with the differences in wavelength are permitted toreconverge, thereby allowing them to couple with eight output waveguidesto guide them to an output ports 18.

To this optical multi-/demultiplexer, light signals having wavelengthsranging from 1545 nm to 1565 nm were input to evaluate thedemultiplexing property of the optical multi-/demultiplexer. As aresult, the intervals of among wavelengths were found 1.6 nm, the losswas found to be 7 dB and the cross talk was found to be 20 dB. When thereliability of characteristics of the optical multi-/demultiplexer wastested in the same manner as described in the aforementioned Example 22,any fluctuation of the characteristics thereof was not recognized.

EXAMPLE 29

FIG. 8 shows a plan view illustrating the structure of a grating typewave filter manufactured in this example. This grating type wave filterwas manufactured by using a solution of the heterocyclic polyimideprecursor prepared in the same manner as described in Example 23 and bythe same procedure as that described in Example 23, thereby fabricatinga buried type waveguide structure on the surface of a metal substrate(not shown). The size in cross-section of the core was set to 8 μm×8 μm,and the waveguide patterns 21 and 22 were constructed such that adirectional coupler having a coupling ratio of 50% is connected with alinear waveguide. In this linear waveguide portion, a refractive indexgrating 2×10⁻³ in difference of refractive index, 0.43 μm in period and2 mm in length was written to obtain the wavelength filter.

A light beam of from an LED light source of 1.31 μm zone was enteredthrough an optical fiber into the input port 23 of the variablewavelength filter, and the characteristics of wavelength that had beenoutput from a drop port 24 was measured by using a spectral analyzer.The transmission characteristics to the drop port 24 under the conditionwhere the temperature of the substrate was 25° C. were 1320 nm incentral wavelength, 0.5 nm in bandwidth, 9 dB in insertion loss and 18dB in quenching ratio. When the temperature of the substrate was raisedto 80° C., the central wavelength became 1310 nm, thus confirming thefact that the grating type wavelength filter of this example was capableof actuating as a variable wavelength filter.

EXAMPLE 30

FIG. 9 shows a perspective view illustrating the structure of abidirectional light transmitting module manufactured in this example. Inthis bidirectional light transmitting module shown in FIG. 9, anelectric wiring layer 28 and an optical waveguide layer 34 are formed onthe surface of a substrate 27.

On the surface of this optical waveguide layer 34, there are disposed alaser diode 29 for transmitting a light beam having a wavelength of 1.3μm, and a photodiode 30 for monitoring the output of light. By usingthese optical semiconductor elements, a conversion component which iscapable of converting transmitting signals from electric signals intolight signals 4 can be constructed. On the surface of the electricwiring layer 28, there is disposed a photodiode 31 for transmitting alight beam having a wavelength of 1.55 μm. By using this opticalsemiconductor element, a transmission component which is capable ofconverting input signals from light signals into electric signals can beconstructed. The optical waveguide layer 34 is provided with an opticalwaveguide 33 consisting of a Y-branched circuit which is provided, at anupper branched portion thereof, with a wavelength-selecting filter 32.

The bidirectional light transmitting module constructed in this mannerwas manufactured by the following procedure. Namely, first of all, theelectric wiring layer 28 was formed on the surface of the substrate 27.Then, by using a solution of the heterocyclic polyimide precursor whichwas prepared in the same manner as described in Example 23 and by thesame procedure as that described in Example 23, the optical waveguidelayer 34 was formed on the surface of the electric wiring layer 28.Further, by lithography, etc., specific regions of the optical waveguidelayer 34, which are assigned to mount optical semiconductor elementssuch as the laser diode 29 for transmitting a light beam and thephotodiode 30 for monitoring the output of light were peeled away, andthen, by dicing, rectangular grooves were formed on the regions forforming a coupling portion between the optical semiconductor elementsand the optical waveguide layer and on the regions where the wavelengthfilter 32 was to be mounted.

Thereafter, an Au/Sn solder layer was formed on the regions of theelectric wiring layer, and the photodiode 31 for transmitting a lightbeam was mounted and electrically connected with the wiring layerthrough the fusion of the solder layer. Subsequently, the wavelengthfilter 32 was fixed to a rectangular groove located at a center of theoptical waveguide layer, and the optical fiber was secured to the Vgroove by using an adhesive. As a result of these processes, it waspossible to manufacture, at a low cost, the bidirectional lighttransmitting module which was excellent in light transmitting propertyand in heat resistance.

The bidirectional light transmitting module was confirmed to exhibit across talk of as small as 35 dB.

EXAMPLE 31

FIG. 10 shows a cross-sectional view illustrating the structure of aphotoelectric composite wiring board manufactured in this example. Inthe photoelectric composite wiring board shown in FIG. 10, semiconductorchips 37 are attached through a microbump 38 to the underside surface ofa supporting substrate 36. This microbump 38 functions as an output portfor the electrodes of the semiconductor chips 37.

The supporting substrate 36 is provided on the top surface thereof withan electric wiring 43 which is electrically connected with theaforementioned semiconductor chips 37 through an electric wiring whichis formed in such a manner as to pierce through the substrate. Throughthe electric connection with an electric wiring 43, a light emittingelement 39 such as a semiconductor laser and LED, as well as a lightreceiving element 40 such as a photodiode are disposed, these elements39 and 40 being insulated by the provision of an insulating layer 41.Further, in such a manner as to electrically connect with the lightemitting element 39 and with the light receiving element 40, an opticalwaveguide layer 42 having inclined faces on the opposite sidewallsthereof is formed on the surface of the insulating layer 41. Thisoptical waveguide layer 42 was manufactured in the same manner as thatdescribed in Example 23 using a solution of the heterocyclic polyimideprecursor which was prepared by the same way as described in Example 23.

The photoelectric composite wiring board constructed in this manner isdesigned such that electric power is fed thereto from a power source(not shown) through the electric wiring 43, thereby enabling thesemiconductor chip 37, the light emitting element 39 and the lightreceiving element 40 to be actuated. When an electric signal is outputto the light emitting element 39 from the semiconductor chip 37, thelight emitting element 39 is actuated so as to convert electric signalsinto light signals, thereby enabling the converted light signals tooutput. The light signals enters into the inclined face formed on one ofthe sidewalls, and to reflect approximately perpendicularly, therebyenabling the light signals to be introduced into the optical waveguidelayer.

The light signal introduced in this manner into the optical waveguidelayer is permitted to transmit as it is, and then, to reflect at theinclined face constituting the opposite sidewall, thus enabling thelight signals to be introduced into the light receiving element 40. Atthis light receiving element 40, the light signals are converted intoelectric signals, which are then output to the semiconductor chip 37. Inthis manner, it is possible, by the optical waveguide layer 42, toenable the light signals to transmit at a high speed between twosemiconductor chips 37.

EXAMPLE 32

FIG. 11 is a perspective view illustrating a light modulatormanufactured in this example. In the light modulator shown in FIG. 11, alower electrode 46, a lower clad layer 47, a core pattern layer 48 andan upper clad layer 49 are successively laminated on a silicon substrate45. Further, upper electrodes 50 are formed on the top surface of thelight modulator.

This light modulator was manufactured according to the followingprocedure. Namely, first of all, a Cr layer having a thickness of 500angstroms and a Au layer having a thickness of 2000 angstroms weresuccessively laminated on the silicon substrate 45 by vacuum vapordeposition method, thereby forming a lower electrode 46. By using asolution of the heterocyclic polyimide precursor which was prepared inthe same manner as described in Example 23 and by the same way as thatdescribed in Example 23, the lower clad layer 47 having a thickness of 5μm and a core layer were successively formed on the surface of the lowerelectrode 46. On the occasion of forming the core layer, the polyimidevarnish employed was formed of a solution which was prepared in the samemanner as in the case of Example 19 and contained 5% by weight, based onthe solid matter, of DRI (Disperse Red 1) as a non-linear opticalmolecule and 10% by weight, based on the solid matter, of 4-hydroxypyridine as a heat cure promoter. This polyimide varnish was spin-coatedon the surface of the lower clad layer 47 and, after the solventincluded therein was removed, the coated layer was prebaked to obtain acore layer.

On the surface of the resultant laminate, an upper Au electrode wasdeposited to a thickness of 2000 angstroms, and then, a DC voltage wasapplied between the upper electrode and the lower electrode in anitrogen atmosphere, thereby performing the poling treatment of thelaminate. Upon finishing the poling, the upper Au electrode was removedand a resist film was deposited thereon. By using a mask of Mach-Zehndertype waveguide pattern, the resist film was subjected toexposure/development treatments to form a dry etching mask pattern.

By reactive ion etching using oxygen gas, the core layer that had beensubjected to the poling treatment was worked to obtain a core patternlayer 48. After the mask pattern was removed, the upper clad layer 49was formed by using the same material as that of the lower clad layer.

Further, the upper electrode 50 was formed on the core waveguide toobtain the light modulator of this example.

Laser beam having a wavelength of 1.3 μm was introduced from thewaveguide input port into the light modulator to evaluate thetransmission loss, electro-optic constant and π shift voltage of themodulator. As a result, the transmission loss was 0.5 dB/cm, theelectro-optic constant was 10 pm/V, and the π shift voltage was 15V.Further, high-frequency signals were applied to the electrodes toobserve the intensity of light to be output to the output port by usinga spectral analyzer, thus confirming a modulation at 100 MHz.

As explained above, it is possible, according to one aspect of thepresent invention, to provide a polyimide optical material which isprovided with sufficient heat resistance and solvent resistance demandedfor the manufacture of an optoelectronic integrated circuit and whichcan be employed as an organic polymer optical material exhibiting anextremely low light transmission loss in the near infrared zone, inparticular, throughout the entire wavelength zone for opticaltransmission (1.0 μm to 1.7 μm). It is also possible to provide asolution of a polyimide precursor, which is useful for synthesizing theaforementioned polyimide optical material. Further, according to anotheraspect of the present invention, it is possible to provide an opticalwaveguide element which can be easily manufactured and is excellent inheat resistance and minimal in light transmission loss.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A polyimide precursor solution comprising a heterocyclic polyamicacid having an unit represented by the following general formula (4),(5) or (6):

(wherein Φ₁s may be the same or different and are individually aquadrivalent organic group, the Φ₁s including at least 0.2 molarequivalent of a quadrivalent hetrocyclic group selected from thefollowing Group (a); Ψ₁s may be the same or different and areindividually a bivalent organic group; and n is a positive integer).

(wherein Φ₂s may be the same or different and are individually aquadrivalent organic group; Ψ₂s may be the same or different and areindividually a bivalent organic group, the Ψ₂s including at least 0.2molar equivalent of a bivalent hetrocyclic group selected from thefollowing Group (b); and n is a positive integer).

(wherein Φ₃s may be the same or different and are individually aquadrivalent organic group, the Φ₃s including at least 0.1 molarequivalent of a quadrivalent hetrocyclic group selected from thefollowing Group (a); Ψ₃s may be the same or different and areindividually a bivalent organic group, the Ψ₃s including at least 0.1molar equivalent of a bivalent hetrocyclic group selected from thefollowing Group (b); and n is a positive integer). Group (a):

Group (b):

(wherein in the above formulas, X may be the same or different and areindividually >O group, >S group or >N—R^(f) group (R^(f) group isperfluoroalkyl group); R may be the same or different and areindividually fluoro group, chloro group, bromo group, iodo group,perfluoroalkyl group, perfluoroalkoxy group, perfluoroalkylthio group,nitro group or cyano group; m is an integer of 1 to 4).
 2. The polyimideprecursor solution according to claim 1, wherein the polyamic acid issynthesized by polymerizing a tetracarboxylic dianhydride and a diaminecompound in an inert gas atmosphere and in an organic polar solventwithout the presence of water.
 3. The polyimide precursor solutionaccording to claim 2, wherein the tetracarboxylic dianhydride is aheterocyclic tetracarboxylic dianhydride is selected from the groupconsisting of a substituted, an unsubstituted heterocyclictetracarboxylic dianhydride, and a combination thereof, wherein all ofhydrogen radicals in the heterocyclic tetracarboxylic dianhydride aresubstituted by a substituent group selected from the group consisting ofa halogen group, a perfluoroalkyl group, a perfluoroalkoxy group, anitro group, and a cyano group.
 4. The polyimide precursor solutionaccording to claim 3, wherein the unsubstituted heterocyclictetracarboxylic dianhydride is selected from the group consisting ofpyrazine tetracarboxylic dianhydride, pyridazine tetracarboxylicdianhydride, furan tetracarboxylic dianhydride, thiophenetetracarboxylic dianhydride, bioxazole tetracarboxylic dianhydride andbithiazole tetracarboxylic dianhydride
 5. The polyimide precursorsolution according to claim 3, wherein the substituted heterocyclictetracarboxylic dianhydride is selected from the group consisting ofpyridine tetracarboxylic dianhydride, phenylene bis(oxazoledicarboxylic) dianhydride, phenylene bis(thiazole dicarboxylic)dianhydride, bifuran tetracarboxylic dianhydride, and bithiophenetetracarboxylic dianhydride.
 6. The polyimide precursor solutionaccording to claim 2, wherein the diamine compound is a heterocyclicdiamine compound is selected from the group consisting of a substituted,a unsubstituted heterocyclic diamine, and a combination thereof, whereinall of hydrogen radicals other than amino group in the heterocyclicdiamine are substituted by a substituent group selected from the groupconsisting of a halogen group, a perfluoroalkyl group, a perfluoroalkoxygroup, a nitro group, and a cyano group.
 7. The polyimide precursorsolution according to claim 6, wherein the unsubstituted heterocyclicdiamine is selected from the group consisting of diaminooxadiazole,diaminothiadiazole, diaminobioxadiazole, diaminobithiadiazole,diaminooxazooxazole, diaminooxazothiazole, diaminothiazolothiazole,diaminothiazolothienothiazole, and diaminothiazolopyrazinothiazole. 8.The polyimide precursor solution according to claim 6, wherein thesubstituted heterocyclic diamine is selected from the group consistingof diaminopyrrole, diaminopyridine, diaminopyridazine,diaminopyrimidine, diaminopyrazine, diaminotriazine, phenylenebis(aminooxadiazole), phenylene bis(aminothiadiazole), phenylenebis(aminopyrazole), diaminobenzobisoxazole, diaminobenzobisthiazole,diaminofuran, diaminothiophene, diaminobioxazole, and diaminobithiazole.9. The polyimide precursor solution according to claim 1, wherein theorganic polar solvent is selected from the group consisting ofN,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide,N,N-dimethoxyacetamide, N-methyl-2-pyrrolidone, N-acetyl-2-pyrrolidone,N-benzyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone,hexamethylphosphortriamide, N-methyl-ε-caprolactam,N-acetyl-ε-caprolactam, 1,2-dimethoxyethane, 1,2-diethoxyethane,bis(2-methoxyethyl)ether, bis(2-ethoxyethyl)ether,1,2-bis(2-methoxyethoxy)ethane, bis[2-(2-methoxyethoxy)ethyl]ether,1-acetoxy-2-methoxyethane, 1-acetoxy-2-ethoxyethane,(2-acetoxyethyl)(2-methoxyethyl)ether, (2-acetoxyethyl)(2-ethoxyethyl)ether, methyl 3-methoxypropionate, tetrahydrofuran, 1,3-dioxane,1,3-dioxolane, 1,4-dioxane, pyrroline, pyridine, picoline,dimethylsulfoxide, sulfolane, γ-butyrolactone, propylene carbonate,phenol, cresol, acetone, methylethyl ketone, methylisobutyl ketone,cyclohexanone, acetonylacetone, and combinations thereof.
 10. Thepolyimide precursor solution according to claim 2, wherein a temperatureof the polymerization reaction is in the range of −20 to 100° C.
 11. Thepolyimide precursor solution according to claim 2, wherein a temperatureof the polymerization reaction is in the range of −5 to 30° C.